Re: [PATCH] KVM: X86: Dynamically allocating MSR number lists(msrs_to_save[], emulated_msrs[], msr_based_features[])

[Xiaoyao Li]

On 11/5/2019 7:30 PM, Paolo Bonzini wrote:
> On 05/11/19 10:20, Chenyi Qiang wrote:
> > The three msr number lists(msrs_to_save[], emulated_msrs[] and
> > msr_based_features[]) are global arrays of kvm.ko, which are
> > initialized/adjusted (copy supported MSRs forward to override the
> > unsupported MSRs) when installing kvm-{intel,amd}.ko, but it doesn't
> > reset these three arrays to their initial value when uninstalling
> > kvm-{intel,amd}.ko. Thus, at the next installation, kvm-{intel,amd}.ko
> > will initialize the modified arrays with some MSRs lost and some MSRs
> > duplicated.
> >
> > So allocate and initialize these three MSR number lists dynamically when
> > installing kvm-{intel,amd}.ko and free them when uninstalling.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
> > ---
> >   arch/x86/kvm/x86.c | 86 ++++++++++++++++++++++++++++++----------------
> >   1 file changed, 57 insertions(+), 29 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index ff395f812719..08efcf6351cc 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1132,13 +1132,15 @@ EXPORT_SYMBOL_GPL(kvm_rdpmc);
> >    * List of msr numbers which we expose to userspace through KVM_GET_MSRS
> >    * and KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST.
> >    *
> > - * This list is modified at module load time to reflect the
> > + * The three msr number lists(msrs_to_save, emulated_msrs, msr_based_features)
> > + * are allocated and initialized at module load time and freed at unload time.
> > + * msrs_to_save is selected from the msrs_to_save_all to reflect the
> >    * capabilities of the host cpu. This capabilities test skips MSRs that are
> > - * kvm-specific. Those are put in emulated_msrs; filtering of emulated_msrs
> > + * kvm-specific. Those are put in emulated_msrs_all; filtering of emulated_msrs
> >    * may depend on host virtualization features rather than host cpu features.
> >    */
> >   
> > -static u32 msrs_to_save[] = {
> > +const u32 msrs_to_save_all[] = {
>
> This can remain static.

How about static const u32 msrs_to_save_all[] ?

Or you think static is enough?

> >   	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
> >   	MSR_STAR,
> >   #ifdef CONFIG_X86_64
> > @@ -1179,9 +1181,10 @@ static u32 msrs_to_save[] = {
> >   	MSR_ARCH_PERFMON_EVENTSEL0 + 16, MSR_ARCH_PERFMON_EVENTSEL0 + 17,
> >   };
> >   
> > +static u32 *msrs_to_save;
>
> You can use ARRAY_SIZE to allocate the destination arrays statically.

It's much better, then we don't need to allocation and free.

> Paolo